Technical Field
The present invention relates to a data storing method for a rewritable non-volatile memory module, and a memory control circuit unit and a memory storage apparatus using the same.
Description of Related Art
The growth of digital cameras, mobile phones, and MP3 players has been rapid in recent years. Consequently, the consumers' demand for storage media has increased tremendously. A rewritable non-volatile memory is one of the most adaptable memories for portable electronic products such as laptop computer due to its data non-volatility, low power consumption, small volume, non-mechanical structure and high read/write speed. A solid state drive (SSD) is a storage apparatus which utilizes a flash memory as its storage medium. For these reasons, the flash memory has become an important part of the electronic industries.
Based on memorable bits of each memory cell, a NAND-type flash memory may be divided into a Single Level Cell (SLC) NAND-type flash memory and a Multi Level Cell (MLC) NAND-type flash memory. Therein, each memory cell of the SLC NAND flash memory is capable of storing one bit of data (i.e., “1” and “0”), and each memory cell of the MLC NAND flash memory is capable of storing two bits of data.
In the NAND-type flash memory, physical pages are formed by a plurality of memory cells arranged in the same word line. Because each memory cell of the SLC NAND flash memory is capable of storing one bit of data, the memory cells arranged on the same word line is corresponding to one physical page in the SLC NAND flash memory.
In comparison with the SLC NAND flash memory, a floating gate storage layer of each memory cell of the MLC NAND flash memory is capable of storing two bits of data. Therein, each storage status (i.e., “11”, “10”, “01” and “00”) includes a Least Significant Bit (LSB) and a Most Significant Bit (MSB). For instance, in the storage status, a value of a first bit counted from the left is the LSB, and a value of a second bit counted from the left is the MSB. Therefore, the memory cells arranged in the same word line can constitute two physical pages. The physical page constituted by the LSBs of said memory cells are referred to as a low physical page, and the physical page constituted by the MSBs of said memory cells are referred to as an upper physical page. Particularly, a writing speed of the low physical page is faster than a writing speed of the upper physical page, and data stored in the low physical page may be lost due to programming fail occurred on the upper physical page.
Particularly, after a flush operation is executed to write data into a buffer memory of a memory storage apparatus to a flash memory module, the data in the buffer memory is erased. Thereafter, in case the data stored in the low physical page is lost due to programming fail occurred on the upper physical page, because the data in the buffer memory is already erased, the data cannot be recovered, such that reliability of the memory storage apparatus may be seriously affected.
Nothing herein should be construed as an admission of knowledge in the prior art of any portion of the present invention. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.